TYSON BIRMANN /
05.01.2011 12:00 PM
Originally featured on BroadcastEngineering.com
Blackmagic Design's UltraScope
When used with HDLink Pro, the waveform monitor allows LUTs to be adjusted in real time.
As a digital image technician (DIT) in the film industry, I recently wrapped production on a prairie western. The main set of the made-for-TV movie was a farmhouse and barn in the middle of golden fields and hills about an hour north of Los Angeles. It was a beautiful setting, but I quickly realized it wasn't an easy setting to shoot in. As long as the characters were outside in the sun or inside the barn or house, things were fine. When there was any combination of the two, however, that became an issue. Because the story took place in the mid-1800s, the interior lighting had to seem natural, or from a candle or flame-based lantern.
The range of digital still hasn't reached that of film. This was most apparent when we were shooting in the barn or cabin with the bright sunshine bouncing off the wheat in the background. Trying to find a balance between the subdued foreground and the explosive background was a constant challenge. Before I get into the solution, I need to talk a little tech.
Monitoring an HD signal directly from a camera is often misleading. People are under the impression that what you see is what you get, but this isn't exactly the case. High-end digital cinema cameras are capable of recording more information than they are outputting to the on-set monitors. The chip can see more than what we know as broadcast legal. This is what look-up tables (LUTs) are for. They allow us to manipulate areas of the image we send to the monitors in order to best simulate the final result. In post production, the colorist will finalize this process. It is the DIT's job to do this on the fly on set.
Meanwhile, back at the ranch …
On set, we were shooting actors in a dark cabin with a bright field through the windows. Ideally, we want them both to be within the limited range of the digital sensor. Normally, we would cover the windows with ND or netting, which would bring the exposure of the two areas closer together.
The problem is that there was no glass in the windows. This, combined with wide depth of field of the 2/3in chip, meant that anything we put in the window would be seen, and we were forced to shoot it clean. At this point (like most things in production), it became about compromise — finding a happy medium of both exposures so that the post-production colorist had the most to work with.
My workstation is almost exclusively Blackmagic Design products. At the heart is the UltraScope. The PC-based waveform is about 80 percent of what I look at in a day on set. In this case, however, I was also relying heavily on the HDLink Pro (also from Blackmagic Design). The HDLink Pro not only converts the HD-SDI signal into DVI so that I can monitor it with low-cost computer monitors, but it also lets me implement and adjust LUTs in real time. For the shots that required a higher dynamic range than the monitors could show, I could adjust the LUTs to show only the top or low end of that range while leaving the recorded image unaffected.
As a result, I was able to explore the full range of the recorded image, meaning I could feel confident that the information recorded to the tape would contain everything the colorist would need to finalize the image effectively. Without using LUTs, this would have been a guessing game — a game that I would rather not play when my job is on the line.
Tyson Birmann is a digital imaging consultant based in Los Angeles.